This invention is directed to a process for methylating phenolic compounds having at least one replaceable hydrogen on the aromatic ring. More particularly, this invention is directed to a process for methylating phenol with methane.
Recently, several different methods have been proposed for methylating phenols. Methylated phenols include: cresols, xylenols and higher methylated phenols like di- and tri-methylphenol.
One such method is taught in an article entitled, "Alkylation of Phenol with Methane Over Solid Acids and Bases," by Tadao Nishizaki and Kozo Tanabe in Chemistry Letters, Pages 149-150, No. 2, February 1973, which is published by the Chemical Society of Japan. This method involves the alkylation of phenol with methane over silica-alumina; or alumina catalyst. The alkylation is conducted at a temperature in the range of 400.degree.-500.degree. C. and at atmospheric pressure. This article also teaches that catalysts such as silica-titania, magnesia-alumina, and magnesium oxide are catalytically inactive in the alkylation of phenol with methane.
Another methylation process is taught in U.S. Pat. No. 3,718,704 (Chapman, et al.). This process for methylating an organic compound, e.g., an aromatic compound with an hydroxy group, includes contacting the methylatable compound with carbon oxide containing reactant gas in the presence of an oxide of Group IB, IIB, and/or VIB metal containing catalyst at a temperature between 400.degree. F. (204.degree. C.) and about 1200.degree. F. (649.degree. C.). This patent also teaches that no appreciable methylated products were obtained when the conditions of the patent were employed, but catalysts were used that were different from those previously stated, for example, various supported catalysts like Group VIII metal oxides.
U.S. Pat. No. 3,822,271 (Lapporte) teaches another methylation process. This process involves methylating alkyl substituted benzenes, aniline, pyridine, and alkyl substituted aniline and pyridine compounds by a mixture of carbon dioxide and hydrogen in the presence of a Fischer Tropsch catalyst like hydrogen reduced oxides or borides of cobalt and/or nickel. The methylation is conducted at a temperature in the range of 150.degree.-450.degree. C. and at a pressure of 1.7-70 atmospheres.
Other methylation processes known in the art prepare ortho-methylphenols by reacting a phenol at a temperature in the range of 300.degree. C.-450.degree. C. with methanol in the presence of ferrite catalysts which contain a divalent metal selected from zinc, magnesium, cobalt, nickel, chromium or cadmium or a catlyst which is a sintered methane-containing of ferric oxide and at least one of the aforementioned divalent metal oxides and a small amount of manganese oxide.
The process for methylating phenols described herein is believed patentable over the known prior art because the prior art does not teach or suggest to one skilled in the art, and actually teaches away from, a method for methylating phenolic compounds with methane in the presence of specific metallic catatlysts.